One step in the fabrication of modem electronic devices such as hybrid integrated circuits (HICs) and printed wiring boards (PWBs) is the use of solder flux, normally a rosin, to insure good bonding of solder elements to copper or aluminum conductors of the devices. After the soldering operation, residual rosin flux must be cleaned from the devices, and for years this was done by using cleaning solvents comprising chlorinated hydrocarbons or chlorinated fluorocarbons (CFCs). The patents of Hayes et al., U.S. Pat. No. 4,740,247, and U.S. Pat. No. 4,640,719, incorporated herein by reference, point out that such solvents are harmful to the environment, and that residual rosin flux can effectively be removed by a cleaning solvent having terpene as its active ingredient, which in turn can be rinsed with water. Terpene compositions are biodegradable, non-toxic and are essentially harmless to the environment.
A system for cleaning PWBs with terpene compositions is described in the paper, "Aqueous and Semi-Aqueous Cleaning Processes," G. M. Wenger et al., AT&T Technical Journal, Vol. 71, No. 2, March/April 1992, pp. 45-51, incorporated herein by reference. It is preferred that the devices be submerged in the terpene composition prior to rinsing, and apparatus for accomplishing this is described. Devices that have been cleaned as described in the Wenger et al. paper have unfortunately been found to be susceptible to failure. Particularly, HIC devices for supporting relatively high voltages have been found to be subject to failure. Microscopic examinations of the components of such devices have shown that many of such failures are due to a precipitate generated within the cleaning solvent during the cleaning operation. When illuminated with ultraviolet light, this precipitate fluoresces and is therefore readily identifiable.